Skip to main content

Historic Preservation - Technical Procedures


Sealing Leaky Wood Double-Hung Windows

Procedure code:



Hspg Prepared For Nps - Sero


Doors And Windows


Wood Double-Hung Windows

Last Modified:



Sealing Leaky Wood Double-Hung Windows




    A.   This procedure includes guidance on sealing leaky windows
         and includes caulking gaps between the wall and the
         frame, filling cracks in the wood, repainting and
         replacing loose window putty.

    B.   Peeling paint, the absence of putty, and open sash joints
         are signs of moisture infiltration into the window sash.
         The wood should be properly sealed against moisture to
         prevent deterioration in wood.

    C.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precautions

         3.   Submittals

         4.   Quality Assurance

         5.   Delivery, Storage and Handling

         6.   Project/Site Conditions

         7.   Sequencing and Scheduling

         8.   General Protection (Surface and Surrounding)

         These guidelines should be reviewed prior to performing
         this procedure and should be followed, when applicable,
         along with recommendations from the Regional Historic
         Preservation Officer (RHPO).



    A.   Caulking Compound (in order of recommended usage):

         1.   Polyurethanes - easily workable; paintable; 15-20
              year life span; limited availability.

         2.   Polysulfides - slow drying; can be sanded and
              painted; highly elastic; limited availability.

         3.   Butyls - paintable but cannot be sanded; 7-10 year
              life span.

         4.   Silicones - some can be painted but generally not

         5.   Acrylic Latex - for exterior work, their use is
              best left to tight, narrow joints; short life span
              especially when compared to polysulfides and

    B.   Polyethylene foam backer rod such as "Ethafoam" SB brand
         backer rod (available at builder's supply houses or
         concrete materials suppliers), or approved equal.

    C.   Linseed oil

    D.   Wood filler (there are four basic types):

         1.   Water-mix Wood Putty:  Easy to tint and fairly
              resilient, but has poor moisture resistance.

         2.   Solvent-based Wood Filler:  Not tintable, but has
              many color choices. A solvent is needed to clean
              any excess or spills. It is difficult to sand, but
              has good adhesion and moisture resistance. It also
              has a problem with shrinkage.

         3.   Acrylic Latex Wood Filler:  Better than water-based
              in adhesion, moisture resistance, and flexibility.
              Apply the filler in layers to avoid shrinkage.

         4.   Two-part Polyester Filler:  Similar to auto body
              filler. It has excellent adherence and moisture
              resistance with minimal shrinkage. It stains
              easily, but is time consuming to prepare.

    E.   Wood water-repellent preservative (see 06310-01-P,
         Section 2.02 Materials, and 06310-01-S)

    F.   Paint (see 06300-01-S)

    G.   Linseed oil putty

    H.   Clean, potable water


    A.   Wire brush

    B.   Natural bristle brushes for oil-based paints:
         Precondition by soaking in raw linseed oil for 24 hours.
         Use nylon bristle brushes for water-based paint.  Do not
         use the same brush for both types of paint.

    C.   Putty knife

    D.   Caulking gun



    A.   Inspect windows periodically, at least yearly.  Check for
         ease of operation, presence and operation of all
         hardware, and cracked or missing putty and glazing.


    A.   Recaulk Gaps Between Window Frame and Wall:

         1.   Renail any loose boards in the window frame.

         2.   Using a wire brush and putty knife, remove any
              loose dirt and debris that may have collected in
              the gap.

         2.   For gaps 3/8 inch or wider, insert a closed-cell
              polyurethane backer rod.

         3.   Push the backer rod into the joint to fill up the
              space behind the caulking.

         4.   Fill gap with a flexible caulking or sealant.
              Apply with a caulking gun until flush with the

         5.   If an oil-based caulk is used, allow the caulk to
              dry for at least 48 hours and then paint.  Paint
              will extend the life of oil-based paint.

    B.   Fill holes and cracks with linseed oil and fill with
         putty (see 06440-04-R for guidance).

    C.   Examine condition of paint.

         1.   If paint has minor cracking or peeling, remove
              loose paint with a wire brush and putty knife and

         2.   If paint deterioration is extensive:

              a.   Remove all paint from window (see 06400-07-R
                   and 06400-09-R for guidance).

              b.   Liberally apply a wood preservative to the
                   wood (see 06310-01-P for guidance).  This acts
                   as a primer for the paint.

              c.   Allow to dry for 24 hours.

              d.   Apply 2 thin coats of paint and allow to dry
                   (see 06300-01-S, 06300-02-R and 09900-07-S for

    D.   Replace Window Putty:

         1.   Remove loose or cracked putty using a putty knife.

         2.   Using a wire brush, remove loose dirt and debris
              from within the putty channel.

         3.   Brush exposed areas with linseed oil.  This will be
              absorbed into the wood and prevent the new  putty
              from drying too quickly and cracking.

         4.   Apply fresh window putty and smooth out with a
              putty knife.

                             END OF SECTION